We aim to detect Lyman-break galaxies (LBGs) by comparing spectra against a known template. In particular, good candidates should:
The first requirement is easier than the second, since we are provided a high-quality LBG template to compare with. If a similarly high-quality template were to be provided for quasars, it should be possible to substantially improve these results.
The method started simple but grew more complex over time with testing.
The main consideration in designing the method was robustness. Every step in the process should be as robust as possible against:
Carefully selected smoothing methods were effective at reducing anticipated noise, convolution matching of absorption troughs was effective at correcting for horizontal shifts, and regressing on quantiles was effective at correcting vertical shifting/scaling. More details are provided below.
The process was carefully constructed and tuned with the help of several R Shiny debugging apps I made (see repo for details). Below is a more in-depth overview:
Steps 5-6 above are kind of a hack. If we had a high-quality quasar template to match against, we may be able to replace it with more elegant code that also achieves higher specificity (this is only a conjecture).
A table of top 1000 results sorted by ranked by composite score can be viewed here.
Plots of some of the best matches are shown below. Most info in the title/label are for my debugging purposes. Notably, the offset index (red-shift correction) and \(A_{\text{peak}}\), \(K_{\text{trans}}\), and \(C\) are shown in the title. The template was shifted down from the spectra for legibility.
For each spectrum, the composite score is also shown on the side for convenience. Initially, I was going to give a (likely very poor) guess for each one what type of astronomical body it may be, but I ultimately decided against it since I really have no idea 🙃
Here are the top 50 or so spectra (with a few visually ruled out). There seem to be quite a few potential quasars in here with broad emission bands CIV and CIII (some of which are quite visible).